The present invention relates to a linear slide bearing and a linear slide table unit constructed by employing the same.
Hitherto, this kind of bearing and table unit which effect a linear guide are widely employed in the sliding part of various general industrial machines such as machining centers, X-, Y- and Z-axes of numerical controlled machine tools, automatic tool changers, automatic welding machines, injection molding machines and industrial robots.
These linear slide bearing and table unit employed in the sliding part of such industrial machines are required to be incorporated in the sliding part with a high accuracy and to be excellent in positioning and repetition accuracies as well as long in life. These properties are particularly important in a linear slide table unit which effects a linear reciprocative motion while bearing a large load. Moreover, the linear slide bearing must be able to readily offer the above-mentioned properties when incorporated in a table unit.
Further, a typical conventional linear slide bearing is arranged such that a pair of raceway grooves are formed in each of shoulders of each track shaft for rolling of load-carrying ball trains on the associated slide block along these raceway grooves, respectively, so that each shoulder of the track shaft is clamped by means of a pair of load-carrying ball trains, thereby to bear loads applied in all directions. Therefore, each track shaft requires machining for forming four grooves. Also, it is necessary to form four endless tracks for balls on the slide block. In consequnce, a large number of processes are required for machining these track shaft and slide block, particularly for grinding and finishing the grooves thereof, resulting in an increase in production cost, disadvantageously.
Furthermore, in such a bearing as described above, if there is a clearance between raceways and balls which bear a load between the slide block and the track shaft, an excessively large impact load is momentarily applied to the bearing by means of a hammering action or a prying and twisting load due to an inertia moment at a direction change in the reciprocating motion, causing a reduction in life. In addition, the positioning and repetition accuracies are deteriorated in accordance with the amount of the clearance.
Accordingly, in the bearing of this kind, it is necessary to apply a preload to the bearing in order to make the above-mentioned clearance negative, thereby to increase the load bearing capacity as well as avoid a momentary application of a large impact load on the bearing for elongation of its life and, moreover, increase the rigidity of the bearing itself. The bearing is, therefore, required to be able to readily apply such a preload.